I think it depends alot on the type of riding you do. I have KN filters on my quad and the wifes, because we ride more sensiable(NOW), the kids get Uni filters because they ride extreme, they go in(or under) water and in mud all day non-stop.I think if you just want to stop dust and moderate water/mud, KN as, any fabric filter will perform as good as stock, but if I was going to ride a dirt bike and seriously abuse it in deep water and mud, I would go through the hassle of foam filters and sticky oil. Another option is a pre-filter that handle water, quite well and slide right over the KNs. That way you get the best of both worlds. KN filters are fabric, I think. Polaris atvs come stock with paper filters, so a KN is definetely a upgrade.